Difficulties in creating a mask that provides a seal between the frame and the swivel connector or elbow have been experienced in the art for some time.
One aim is to make a seal that achieves minimal leak over the tolerance range expected from the manufacturing process of the elbow and frame. In many prior art masks, this seal is attempted by controlling the tolerances associated with the elbow and frame very closely to provide a minimum clearance between the elbow and frame while still allowing rotation. It has been found that it is difficult to control leak at tolerance limits in these designs.
For any material having tolerances that are harder to control, the problem of achieving a suitably low clearance for sealing between the elbow and frame is exacerbated. Polypropylene is one example. Parts made of polypropylene must be dimensioned with larger tolerances because this material is harder to mold to precise dimensions. Therefore, minimizing leak at tolerance limits in a controlled clearance type seal with polypropylene parts is very difficult.
Another aim is to reduce friction when the swivel connector or elbow is rotated. However, a small amount of friction is considered advantageous. This has been a difficult balance to achieve to date.
Another aim is to provide a sealing arrangement that does not substantially increase the cost of goods.